Does the Redfield ratio infer nutrient limitation in the macroalga Spirogyra fluviatilis?

Abstract

1. The cellular nutrient contents of microalgae, when growing at or approaching maximum rates, approximate the Redfield C : N : P (molar) ratio of 106 : 16 : 1. Deviations from this optimal ratio can be used to infer nutrient limitation of microalgal growth. However, this ratio may not be applicable to macroalgae, which are distinguished from microalgae by forming a thallus that is a discrete structure visible to the naked eye. The utility of the Redfield ratio to infer nutrient limitation of the growth of macroalgae was tested for Spirogyra fluviatilis in a field experiment conducted in tropical Australia. 2. The optimal cellular C : N : P ratio for S. fluvialitis was estimated by means of in situ nutrient addition. This was compared with S. fluvialitis cellular ratios determined from eight sites with a wide range of soluble N concentrations (<1-90 lg L )1 ), a smaller range of soluble P concentrations (5-12 lg L )1 ), and soluble molar N : P ratios of 0.11-27. 3. Spirogyra fluviatilis had an optimal molar C : N : P ratio of 1800 : 87 : 1 which differs substantially from the Redfield ratio, and suggests that the latter ratio is not applicable to this macroalga. Concentrations of N and P in the river deviated from the optimal N : P ratio of 87 : 1, inferring nutrient limitation of growth. 4. C : P and C : N ratios of S. fluviatilis varied in accordance with general stoichiometric relationships for autotrophs under nutrient limitation of growth. Ratios of C : P and C : N increased, respectively, with increased severity of P-and N-limitation. Additionally, C : P ratios increased with increased N : P ratios, whilst the C : N ratio increased with decreased N : P ratios. The C : N molar ratio however was an insensitive indicator of nutrient depletion compared with the C : P ratio. Under N-limitation of growth, luxury amounts of P were stored by S. fluviatilis. 5. In aquatic environments where macroalgae are sufficiently abundant to be sampled, their cellular carbon, nitrogen and phosphorus stoichiometry can be used to infer nutrient limitation of growth when their optimal C : N : P ratio is known.

Management of agricultural practices results in declines of filamentous algae in the lake littoral

“…Such low ratios were rarely measured for the streams in the present study, giving further credence to the conclusion that P was the limiting nutrient for littoral algal growth. In contrast to the Conesus Lake results, studies by Townsend et al (2008) on a tropical species of Spirogyra that inhabits streams and rivers of Australia indicated that both N and P could alternately limit growth. Optimal cellular N:P ratios for S. fluviatilis were 87:1, indicating a higher N requirement than predicted by the Redfield ratio of 16:1 that is typical of microalgae.…”

“…The possibility that N limitation may be controlling filamentous algal cover in some sub-watersheds is interesting and plausible. In addition to the work of Townsend et al, (2008) showing variations in nutrient limitation on Spirogyra, mesocosm experiments with benthic algae, organisms that are often a few centimeters below surficial filamentous algae in the water column, have demonstrated that large amounts of N and P are removed from the water column and that both may be limiting for growth (Havens et al, 1999, McDougal et al, 1997. The design and consequently the results of the watershed manipulation experiments reported here do not allow or indicate whether N or P or both were limiting to littoral algal growth in Conesus Lake while correlation analyses have to be viewed as suggestive.…”

“…Algal samples were collected from a variety of habitats, and among these approximately half appeared to be N limited. Locally high N concentrations in other habitats resulted in P limitation (Townsend et al, 2008).…”

Temporal variation in benthic primary production in streams of the Australian wet–dry tropics

“…This has been found to be related to local-scale habitat factors such as canopy cover, river orientation and substrate, with higher photosynthetically active radiation (PAR) strongly correlated with higher GPP (Mulholland et al, 2001), and often greater productivity on cobble substrate compared with sand (Fellows et al, 2006). In Australia's wet-dry tropics during the dry season, most rivers are oligotrophic (Brodie & Mitchell, 2005) and PAR is often high and thus primary production has been shown to be nutrient-rather than light-or carbon-limited (Webster et al, 2005;Ganf & Rea, 2007;Townsend et al, 2008). Primary production and factors limiting production are generally measured in the dry season, and thus, knowledge of the dynamics in GPP and algal biomass over the annual cycle is limited.…”

Some silkweeds (Zygnemataceae, Zygnemales, Charophyceae) from the Upper Murrumbidgee River catchment

“…Occasionally papers are published which include descriptions and bio-geographical information (Townsend et al 2008) but generally the baseline information is unavailable, being held in departmental records (Skinner 2008). It is rare to find published papers with detailed and floristic content (May andPowell 1986, Entwisle 1989a, b).…”